Invention through bricolage: epistemic engineering in scientific communities

It is widely recognised that knowledge accumulation is an important aspect of scientific communities. In this essay, drawing on a range of material from theoretical biology and behavioural science, I discuss a particular aspect of the intergenerational nature of human communities – “virtual collaboration” (Tomasello 1999) – and how it can lead to epistemic progress without any explicit intentional creativity (Henrich 2016). My aim in this paper is to make this work relevant to theorists working on the social structures of science so that these processes can be utilised and optimised in scientific communities

Removing the Spin-Triplet Loss Pathway in Organic Solar Cells: A Strategy to Enhance Radiative Efficiency and Minimise Energy Loss

In this dissertation, we describe our work into suppressing the formation of triplet excitons in organic solar cells, created as a result of unavoidable non-geminate charge recombination processes. Triplet excitons represent a major non-radiative loss pathway in organic solar cells and through this work, we demonstrate tactics to reduce the non-radiative decay of photo-generated charges and thereby enhance the radiative efficiency of their decay processes. As the ideal solar cell would have only voltage loss resulting from the radiative recombination of charge carriers, we aim to decrease the magnitude of the non-radiative voltage losses in organic solar cells. In this work, we present two distinct strategies to achieve this: i. The kinetic suppression of the back electron transfer process from the triplet charge transfer state to the local triplet state, so it is out-competed by re-dissociation of the charge transfer state into free charges. ii. The use of low-exchange energy materials that allow for the simultaneous creation of a charge transfer state that is close in energy to the lowest singlet state to minimise the energy loss associated with charge generation, but still below the energy of the lowest triplet state, thermodynamically forbidding the formation of any local triplet states. The first study investigates two closely-related high-performing organic solar cells that show an extremely low total voltage loss. Through detailed investigations of these donor-acceptor blends, we determine that the low voltage loss can be attributed to enhanced levels of radiative recombination. Further, we show that over the timescales of non-geminate recombination there is no observable formation of triplet excitons in the blend. Accrediting the enhanced radiative recombination to the absence of the non-radiative triplet loss pathway, we explore the factors controlling the rate of the back electron transfer process that leads to triplet formation. From our preliminary calculations, we determine that the factor most likely responsible for a slow back electron transfer rate is the electronic coupling between the triplet charge transfer state and the molecular triplet exciton. If the rate of this process is sufficiently slowed, it will be out-competed by the rate of the re-dissociation of the charge transfer state, leading to the kinetic suppression of triplet exciton formation. Having determined the efficacy of removing the triplet loss pathway in enhancing the radiative efficiency of recombination, the next two investigations focus on the second strategy discussed: thermodynamically forbidding triplet formation. For this, we utilise two different low exchange energy organic thermally activated delayed fluorescence materials as electron acceptors that are paired with wider band gap, high triplet energy donors. Through spectroscopic studies of the blends, we demonstrate that charge generation can proceed efficiently from both components, a prerequisite for efficient solar cell operation. Furthermore, the excellent radiative efficiencies and low non-radiative voltage losses of the blends confirms that this is indeed an effective route to improve the performance of organic solar cells.EPSRC studentshi

ABO blood type, factor VIII, and incident cognitive impairment in the REGARDS cohort

OBJECTIVE: To assess the relationships among ABO group, factor VIII (FVIII), and incident cognitive impairment in a large, prospective cohort study of black and white adults in the United States using a nested case-control design. METHODS: Incident cognitive impairment was defined using cognitive domain tests over a mean follow-up of 3.4 years. ABO blood group was measured by genotyping in a nested case-control sample of 495 cases with cognitive impairment and 587 controls. RESULTS: Those with blood group AB and those with higher FVIII had an increased risk of cognitive impairment, adjusting for age, race, region, and sex (respective odds ratios 1.82, 95% confidence interval [CI] 1.15-2.90; and 1.24, 95% CI 1.10-1.38 for 40 IU/dL higher FVIII). Mean FVIII was higher in those with blood type AB (142 IU/dL; 95% CI 119-165) compared with O (104 IU/dL; 95% CI 101-107), and FVIII mediated 18% of the association between AB group and incident cognitive impairment (95% CI for mediation -30% to 68%). CONCLUSIONS: Blood group AB and higher FVIII were associated with increased incidence of cognitive impairment in this prospective study. The association of blood group AB with incident cognitive impairment was not significantly mediated by FVIII levels

Thermally Pulsing Asymptotic Giant Branch Star Models and Globular Cluster Planetary Nebulae I: The Model

Thermally pulsing asymptotic giant branch models of globular cluster stars are calculated using a synthetic model with the goal of reproducing the chemical composition, core masses and other observational parameters of the four known globular cluster planetary nebulae as well as roughly matching the overall cluster properties. The evolution of stars with an enhanced helium abundance ($Y$) and blue stragglers are modeled. New pre-thermally pulsing asymptotic giant branch mass-losses for red giant branch and early asymptotic giant branch stars are calculated from the Padova stellar evolution models \citep{berta,bertb}. The new mass-losses are calculated to get the relative differences in mass-losses due to enhanced helium abundances. The global properties of the globular cluster planetary nebula are reproduced with these models. The metallicity, mass of the central star, overall metallicities, helium abundance and the nebular mass are matched to the observational values. Globular cluster planetary nebulae JaFu 1 and JaFu 2 are reproduced {\it by assuming progenitor stars} with masses near the typical main sequence turn-offs of globular clusters and with enhanced helium abundances very similar to the enhancements inferred from fitting isochrones to globular cluster colour-magnitude diagrams. The globular cluster PN GJJC-1 can be roughly fit by a progenitor star with very extreme helium enhancement ($Y\approx0.40$) near the turn-off producing a central star with the same mass as inferred by observations and a very low nebular mass. The abundances and core mass of planetary nebula Ps 1 and its central star (K648) are reproduced by a blue straggler model. However, it turned out to be impossible to reproduce its nebular mass and it is concluded some kind of binary scenario may be needed to explain K648.Comment: 14 pages, 8 figures, accepted for publication in MNRA

High stability and luminescence efficiency in donor-acceptor neutral radicals not following the Aufbau principle.

With their unusual electronic structures, organic radical molecules display luminescence properties potentially relevant to lighting applications; yet, their luminescence quantum yield and stability lag behind those of other organic emitters. Here, we designed donor-acceptor neutral radicals based on an electron-poor perchlorotriphenylmethyl or tris(2,4,6-trichlorophenyl)methyl radical moiety combined with different electron-rich groups. Experimental and quantum-chemical studies demonstrate that the molecules do not follow the Aufbau principle: the singly occupied molecular orbital is found to lie below the highest (doubly) occupied molecular orbital. These donor-acceptor radicals have a strong emission yield (up to 54%) and high photostability, with estimated half-lives reaching up to several months under pulsed ultraviolet laser irradiation. Organic light-emitting diodes based on such a radical emitter show deep-red/near-infrared emission with a maximal external quantum efficiency of 5.3%. Our results provide a simple molecular-design strategy for stable, highly luminescent radicals with non-Aufbau electronic structures.Includes EPSRC

Short contacts between chains enhancing luminescence quantum yields and carrier mobilities in conjugated copolymers

Abstract: Efficient conjugated polymer optoelectronic devices benefit from concomitantly high luminescence and high charge carrier mobility. This is difficult to achieve, as interchain interactions, which are needed to ensure efficient charge transport, tend also to reduce radiative recombination and lead to solid-state quenching effects. Many studies detail strategies for reducing these interactions to increase luminescence, or modifying chain packing motifs to improve percolation charge transport; however achieving these properties together has proved elusive. Here, we show that properly designed amorphous donor-alt-acceptor conjugated polymers can circumvent this problem; combining a tuneable energy gap, fast radiative recombination rates and luminescence quantum efficiencies >15% with high carrier mobilities exceeding 2.4 cm2/Vs. We use photoluminescence from exciton states pinned to close-crossing points to study the interplay between mobility and luminescence. These materials show promise towards realising advanced optoelectronic devices based on conjugated polymers, including electrically-driven polymer lasers

Specialist Respiratory Outreach : a case-finding initiative for identifying undiagnosed COPD in primary care

Acknowledgments This report is independent research funded by the National Institute for Health Research Wessex ARC. The views expressed in this publication are those of the author(s) and not necessarily those of the National Institute for Health Research or the Department of Health and Social Care. We are very grateful to Optimum Patient care and their team for their help and support with the data extraction and application of the case-finding risk score. We would also like to thank: The participants, Mark Stafford-Watson (PPI) in memorial, Colin Newell, Dr Fiona McKenna, Dr Andy Powell, Dr Helen Myers, Dr Stuart McKinnes, Dr Mark Williams, Dr Louisa Egbe, Dr Richard Baxter, Dr Sarah A’Court, Dr Elisabeth Willows, Dr Gareth Morris, Dr Ford, Dr Kate Lippiett, Wessex Clinical Research Network, West Hampshire CCG and Southampton City CCGPeer reviewedPublisher PD

Electron spin resonance resolves intermediate triplet states in delayed fluorescence.

Molecular organic fluorophores are currently used in organic light-emitting diodes, though non-emissive triplet excitons generated in devices incorporating conventional fluorophores limit the efficiency. This limit can be overcome in materials that have intramolecular charge-transfer excitonic states and associated small singlet-triplet energy separations; triplets can then be converted to emissive singlet excitons resulting in efficient delayed fluorescence. However, the mechanistic details of the spin interconversion have not yet been fully resolved. We report transient electron spin resonance studies that allow direct probing of the spin conversion in a series of delayed fluorescence fluorophores with varying energy gaps between local excitation and charge-transfer triplet states. The observation of distinct triplet signals, unusual in transient electron spin resonance, suggests that multiple triplet states mediate the photophysics for efficient light emission in delayed fluorescence emitters. We reveal that as the energy separation between local excitation and charge-transfer triplet states decreases, spin interconversion changes from a direct, singlet-triplet mechanism to an indirect mechanism involving intermediate states

Long-lived and disorder-free charge transfer states enable endothermic charge separation in efficient non-fullerene organic solar cells

Funder: HKU | University Research Committee, University of Hong Kong (HKU Research Committee); doi: https://doi.org/10.13039/501100003802Abstract: Organic solar cells based on non-fullerene acceptors can show high charge generation yields despite near-zero donor–acceptor energy offsets to drive charge separation and overcome the mutual Coulomb attraction between electron and hole. Here, we use time-resolved optical spectroscopy to show that free charges in these systems are generated by thermally activated dissociation of interfacial charge-transfer states that occurs over hundreds of picoseconds at room temperature, three orders of magnitude slower than comparable fullerene-based systems. Upon free electron–hole encounters at later times, both charge-transfer states and emissive excitons are regenerated, thus setting up an equilibrium between excitons, charge-transfer states and free charges. Our results suggest that the formation of long-lived and disorder-free charge-transfer states in these systems enables them to operate closely to quasi-thermodynamic conditions with no requirement for energy offsets to drive interfacial charge separation and achieve suppressed non-radiative recombination